The present invention relates to the technical field of catalytic condensation or coupling of alcohols or carbonyl compounds with CH-acidic compounds, in particular for producing higher alcohols, aldehydes, ketones, aromatics and/or alkanes and also mixtures thereof.
In particular, the present invention relates to a method for the catalytic condensation or coupling of organic compounds containing oxo and/or hydroxyl functions with CH-acidic compounds.
In addition, the present invention relates to products and product mixtures, in particular alcohols, aldehydes, ketones, alkanes and/or aromatics, and also mixtures thereof, which are obtainable by the method according to the invention.
Furthermore, the present invention relates to the use of the products or product mixtures according to the invention as combustibles or transport fuels and also as chemicals for private and industrial purposes.
Finally, the present invention relates to the use of an activated carbon substrate provided with at least one metal as catalyst for the catalytic condensation or coupling of organic compounds containing oxo and/or hydroxyl functions with CH-acidic compounds.
A central problem of chemical-industrial production is the synthesis of longer-chain nonpolymeric compounds starting from short-chain, inexpensive and also industrially available starting materials for the purpose of producing high-value chemical products, such as, for example, surfactants, additives, or else certain combustible fractions. In this connection, in particular, higher-molecular-weight alcohols are of importance.
One possibility of generating, for example, high-molecular-weight alcohols, is what is termed the Guerbet reaction, in which primary or secondary alcohols are coupled, in particular in a basic environment, and mostly branched primary alcohols are obtained.
In the reaction named after the chemist Marcel Guerbet, in the actual meaning it is an organic reaction in which primary or secondary alcohols are reacted catalytically with elimination of one equivalent of water to form beta-alkylated dimerized alcohols, wherein, usually, hydrogenation catalysts known per se such as, for example, what is termed Raney nickel, or alkali metal hydroxides or alkali metal alkoxides are used.
The production of what are termed these Guerbet alcohols proceeds from the prior art usually in a homogeneous catalytic process in which principally alkali metal and alkaline earth metal catalysts in the form of their hydroxides are used, which must then be separated off after the synthesis and thus generate waste. In the process, the synthesis proceeds under elevated pressure and at temperatures which are usually below the boiling point of the starting materials, which very greatly restricts the flexibility of the method for low-boiling alcohols (cf. DE 693 16 349 T2, EP 0 299 720 A2, U.S. Pat. No. 766,677 A, US 2010/0298613 A1, WO 91/04242 A1 and WO 2011/054483 A1).
From these higher alcohols, in subsequent reaction steps, further products such as, for example alkanes, can be produced. In particular, it is in addition possible in complex processes to obtain alkane mixtures having comparable properties to aviation gasoline, in particular kerosene.
On account of the enormous demand for aircraft kerosene, what is termed JET-A1 or Jetfuel, of about 200 million tonnes worldwide—in Germany alone, over 8.5 million tonnes were consumed in 2010—for provision of the required alkanes on a biogenic basis, the conversion of a widely available, favorable and regenerative raw material is necessary. Also, in particular against the background of increasing trade with CO2 certificates, the production of a sustainable biokerosene or admixture thereof to fossil-produced kerosene is of very great interest to the aviation industry.
Usually, the paraffins used as aviation fuels are obtained in the form of what is termed a middle distillate of crude oil refining and consist, inter alia, of approximately 35% by mass of branched and unbranched C8-C15 alkanes.
Known processes, for producing kerosene on the basis of renewable raw materials are principally based on the hydrogenation or hydrotreating of vegetable oils. However, principally unbranched and saturated alkanes form, the boiling point and freezing point range of which differs markedly from fossil-based kerosene. Therefore, additional isomerization and hydrocracking steps are necessary.
To date there still does not exist a method to produce kerosene by direct catalytic condensation from alcohols, in particular not on the basis of renewable raw materials.
In addition, higher alcohols, in particular branched alcohols (what are termed Guerbet alcohols) and linear alcohols, and also alkanes and alkenes in the boiling range of Jetfuel cannot yet be produced by a one-step heterogeneously catalyzed condensation without hydrogen from, in particular, bio-based shorter-chain alcohols. Therefore, dehydration, for example, to form alkenes and oligomerization of the alkenes must be provided upstream, in order in this manner to build up the required carbon chain. In order to generate kerosene, hydrogenation must be carried out afterward, or producing alcohols, hydration must be performed again (cf. in particular EP 0 099 690 A2).
According to the prior art, higher alcohols can equally be produced by aldol condensation, wherein homogeneous catalysts, such as inorganic hydroxides, or similarly strong bases, are used. However, this route has not been usable economically to date for kerosene production.
The multistage production of bio-based kerosene is also possible from bio-based furfurals or derivatives and ketones thereof, such as, e.g., acetone. The furfurals required for this purpose must however first be obtained from lignocellulose in a complex manner.
In further methods for producing kerosene according to the prior art, in part oxygen-containing compounds are used in such a manner that the resultant products likewise do not conform to the valid standard for kerosene or aviation fuels, in particular jet fuel. Such a method is described, for example, in EP 1 218 472 A1.
In addition, the production of aviation gasoline via dehydration of isobutanol and other alcohols produced by fermentation, in particular what are termed fusel alcohols, and the following oligomerization of the resultant alkenes with subsequent hydrogenation is known, such as, for example, as described in the IATA 2010 Report on Alternative Fuels (December 2010), Ref. No.: 9709-03, ISBN 978-92-9233-491-8.
Since the condensation in particular of alcohols and aldehydes to give higher alcohols, alkanes etc. and optionally the further reaction thereof, at least in theory, promises an accessible route to higher molecular compounds, in the prior there has been no lack of attempts to improve the existing condensation methods or develop novel methods on this basis.
CA 2 298 545 A1 relates to a method for producing metal-free Guerbet alcohols, wherein primary or secondary alcohols are condensed in the presence of alkaline catalysts or heavy metal catalysts at high temperatures with removal of the resultant water.
DE-A 29 12 068 relates to a method for producing hydrocarbons in which alcohols are reacted by means of transition metal or heavy metal catalysts. In the method described, principally olefins, and also to a lesser extent, aromatics, are obtained as products.
In addition, EP 1 052 234 A1 relates to a method for producing starting materials or raw materials for the chemical industry, and also high-octane motor fuels by catalytic reaction of ethanol by means of a calcium phosphate catalyst which contains an activating metal.
The scientific publication “Synthesis of Biogasoline from Ethanol over Hydroxyapatite Catalysts”, T. Tsuchida, T. Yoshioka, S. Sakuma, T. Takeguchi and W. Ueda, Ind. Eng. Chem. Res. 47, pages 1443 to 1452 (2008) relates to the production of bio-based motor fuels from ethanol.
In addition, the scientific publication “Integration of C—C coupling reactions of biomass-derived oxygenates to fuel-grade compounds”, E. I. Gürbüz, E. L. Kunkes and J. A. Dumesic, Applied Catalysis B: Environmental 94, pages 134 to 141 (2010) relates to the reaction of oxygenated organic compounds obtained from biological processes to produce motor fuels.
Similarly, the scientific publication “Conversion of biomass-derived butanal into gasoline-range branched hydrocarbon over Pd-supported catalysts”, S. M. Kim, M. E. Lee, J.-W. Choi, D. J. Suh and Y.-W. Suh, Catalysis Communications 16, pages 108 to 113 (2011) relates to the reaction of butanal obtained by biosynthesis to form motor fuels.
Furthermore, the scientific publication “Combined solid base/hydrogenation catalysts for industrial condensation reactions”, F. King and G. J. Kelly, Catalysis Today 73, pages 75 to 81 (2002), relates to catalysts for industrially employed condensation reactions.
The scientific publication “Reactions of methanol and higher alcohols over H-ZSM-5”, A. C. Gujar, V. K. Guda, M. Nolan, Q. Yan, H. Toghiani and M. G. White, Applied Catalysis A: General 363, pages 115 to 121 (2009), relates to condensation reactions of methanol and higher alcohols.
Finally, the scientific publication “Hydrotalcide-derived mixed oxides as catalyst for different C—C bond formation reactions from bioorganic materials”, S. Ordóñez, E. Díaz, M. León and L. Faba, Catalysis Today, Vol. 167, pages 71 to 76 (2011), firstly describes the self-condensation of acetone and also the self-condensation of ethanol in each case in the gas phase, and secondly describes the aldol condensation of furfuryl alcohol with acetone in the liquid phase. The condensation reactions of acetone or ethanol in the gas phase can only be carried out in greatly diluted gas streams and deliver extremely low conversion rates. Also, the liquid phase reaction of furfuryl alcohol and acetone can only be carried out with extremely low reactant concentrations and requires at least 24 hours of reaction time in order to achieve conversion rates of approximately 70%, wherein the product selectivity is extremely low.
The above-described methods are therefore not suitable for synthesizing chemical compounds, in particular not on an industrial scale.
The above-described methods of the prior art all have the disadvantage that condensation reactions of alcohols and carbonyl compounds only proceed in low yields, in particular only in low space-time yields, or only with low space velocities, and so these methods are of low efficiency and cannot be carried out in a worthwhile manner economically.
In addition, in the methods of the prior art, a process procedure is required which is complex to implement, with dilution of the reactants with inert gas or solvents, such as water, for example. Most of the above-described methods of the prior art in addition use catalyst systems having catalyst service lives which are inadequate under large-scale conditions. Also, it is frequently difficult to provide controllable reaction conditions, in such a manner that yields and product mixtures cannot be obtained in a reliable manner. Most of the methods described are therefore unsuitable for large-scale applications.